The present invention relates to a polymorph of 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine having the formula (I): 
having a PXRD pattern substantially as defined hereinafter:
As detailed in WO 01/27113, 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine is a potent and selective cGMP PDE5 inhibitor and is especially useful in the treatment of inter alia male erectile dysfunction.
For successful utility within the pharmaceutical industry it is critical that the physicochemical properties of an active material are either known or can be reasonably predicted throughout the necessary processes during both its manufacture and pharmaceutical processing as well as during its shipping, storage and eventual therapeutic use. In some cases compounds can exhibit desirable medicinal properties which cannot be translated directly into a suitable pharmaceutical composition because the active compound itself has unsatisfactory physical properties such as for example poor chemical or processing properties. As such, stable, crystalline materials are highly desirable for use in the pharmaceutical industry as crystalline materials are, in general, more stable than their amorphous counterparts, they have a finite structure which can be reproducibly characterised by X-ray diffraction which can be used to identify the presence of a specific polymorphic form.
The present invention provides the crystal structure of 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5yl]-3-pyridylsulfonyl}-4-ethylpiperazine.
The crystalline material of 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine as defined herein may also be referred to as a non-solvated a product of 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine wherein a non-solvated product as defined herein means a product which has essentially no retained solvent bound within the crystal lattice or otherwise entrapped or engaged within the crystals. Solvent retained on the surface of the crystal lattice is not included within the definition of retained solvent, although it is preferred that the crystalline material of the present invention does not retain solvent on the surface. Essentially no retained solvent as defined herein means that there is less than 1%, preferably less than about 0.85%, more preferably less than about 0.3% and especially from 0 to 0.25% total retained solvent within the crystal lattice structure or entrapped within the crystals.
The crystals of 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine having the XRD pattern as defined hereinafter have a high melting point and early investigations show that they are non-hygroscopic, are stable and have good formulation properties.
The preparation of 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine having the formula (I) according to the present invention may be carried out as illustrated in the Example and Preparations sections hereinafter.
The XRD pattern of 1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine having the formula (I) can be characterised according to the method detailed hereinafter.
X-Ray Diffraction